Disable GCC "may be used uninitialized" on a particular variable

Try doing this:

 #pragma GCC diagnostic ignored "-Wuninitialized"
        foo(b);         /* no diagnostic for this one */

This pragma comes in three interesting and helpful flavors : warning, error, ignored. See 6.56.10 Diagnostic Pragmas for their usages. The link says,

GCC allows the user to selectively enable or disable certain types of diagnostics, and change the kind of the diagnostic. For example, a project's policy might require that all sources compile with -Werror but certain files might have exceptions allowing specific types of warnings. Or, a project might selectively enable diagnostics and treat them as errors depending on which preprocessor macros are defined.

The accepted answer has two big problems that requires more than a comment. First, it deactivates the warning for the whole file. If that pragma resides in a header, probably for more. Warnings are useful and if it is indeed a false positive, one should disable the warning for a bunch of code as small as possible.

Then the warning in the OP is "maybe uninitialized" which is deactivated by -Wmaybe-uninitialized, as opposed to -Wuninitialized.

#pragma GCC diagnostic push                             // save the actual diag context
#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"  // disable maybe warnings
function() or int variable;                             // impacted section of code
#pragma GCC diagnostic pop                              // restore previous diag context